Difference between revisions of "Protozoa"

Revision as of 18:31, 15 November 2008

INFECTIOUS AGENTS AND PARASITES PARASITES

Introduction

Balantidium coli - trofozoite and cyst - Wikimedia Commons

Flagella of E.coli - Nicolle Rager Fuller, National Science Foundation

All protozoa are unicellular eukaryotic organisms which store their genetic information in chromosomes in a nuclear envelope. Protozoa are classified depending on their structure and life cycle. This reflects the similarities of the diseases which they cause.

Protozoa usually range from 10μm-50μm but can grow up to 1mm. Thus, they are usually observed and classified using a microscope.

Protozoa multiply sexually, asexually and can also use a combination of both, for example, the coccidia class. Replication can be by binary or multiple fission. Different protozoa use different forms of motility, including flagella, cilia, pseudopodia and gliding.

Structure and function

Motile

Organelles and otehr cellular structures enable the protozoa to lead an independent exsistence

Cilia
- Fine, short hairs covering the protozoal surface
- Hairs beat in unison to enable the protozoa to move
- Wafts food towards the cytostome (mouth opening)
- E.g. Balantidium

Flagellum
- Contractile fibre
- Contracts in a whip like motion to propel protozoa
- Attached to body of protozoa by an undulating membrane
- E.g. Trypanosoma

Pseudopodia
- Extensions of the cellular cytoplasm
- Cytoplasm flows into the pseudopodia allowing movement of the protozoa
- Also acts in a phagocytic manner surrounding food particles and enclosing it in a vacuole
- E.g. Entamoeba

Gliding
- No obvious means of locomotion
- E.g. Eimeria

Nutrition and digestion

Pinocytosis - Mariana Ruiz Villarreal

Pinocytosis
- Droplets of fluid taken into the cell
- Generates small vesicles
- Usually used for extracellular fluid ingestion
- Requires ATP

Phagocytosis
- Larger particles of matter taken into the cell
- Usually solid particles ingested

Cell membrane envelops the fluid or food taking it into the cell

Lysosomes fuse with the fluid/food initiating digestion

Diffusion through the cell membrane allows excretion of metabolic products

Life Cycle

Most protzoal reproduction is asexual using binary fission, schizogony and sporogony

Some protozoa also use sexual reproduction called gametogony

In some species, sexual and asexual reproduction occurs in the same host, whilst in others asexual reproduction occurs in the vertebrate host and sexual reproduction in the arthropod vector

Homogenous
- Parasite uses a single host species during its life cycle (direct)
- E.g. Eimeria

Heteroxenous
- Parasite uses more than one host during its life cycle (indirect)
- E.g. Trypanosomes

Facultatively heteroxenous
- Parasite may use more than one host during its life cycle but this is not essential
- E.g. Toxoplasma gondii

Example Coccidian Life Cycle

The following refers specifically to the life cycle of Coccidia spp.

Protozoa of Veterinary Importance

Coccidia

Tissue cyst-forming coccidia

Piroplasmida

Cryptosporidium

Babesia

Leishmania involved in skin infections

@@ Line 1: / Line 1: @@
-#REDIRECT[[:Category:Protozoa]]
+{{toplink
+|backcolour =
+|linkpage =Infectious agents and parasites
+|linktext =INFECTIOUS AGENTS AND PARASITES
+|pagetype=Bugs
+|sublink1=Parasites
+|subtext1=PARASITES
+}}
+==Introduction==
+[[Image:Balanditium.jpg|thumb|right|150px|Balantidium coli - trofozoite and cyst - Wikimedia Commons]]
+[[Image:Flagella.jpg|thumb|right|150px|Flagella of ''E.coli'' - Nicolle Rager Fuller, National Science Foundation]]
+All protozoa are unicellular eukaryotic organisms which store their genetic information in chromosomes in a nuclear envelope. Protozoa are classified depending on their structure and life cycle. This reflects the similarities of the diseases which they cause.
+Protozoa usually range from 10μm-50μm but can grow up to 1mm. Thus, they are usually observed and classified using a microscope.
+Protozoa multiply sexually, asexually and can also use a combination of both, for example, the coccidia class. Replication can be by binary or multiple fission. Different protozoa use different forms of motility, including flagella, cilia, pseudopodia and gliding.
+==Structure and function==
+*Motile
+*Organelles and otehr cellular structures enable the protozoa to lead an '''independent exsistence'''
+*Cilia
+**Fine, short hairs covering the protozoal surface
+**Hairs beat in unison to enable the protozoa to move
+**Wafts food towards the cytostome (mouth opening)
+**E.g. ''Balantidium''
+*Flagellum
+**Contractile fibre
+**Contracts in a whip like motion to propel protozoa
+**Attached to body of protozoa by an '''undulating membrane'''
+**E.g. ''Trypanosoma''
+*Pseudopodia
+**Extensions of the cellular cytoplasm
+**Cytoplasm flows into the pseudopodia allowing movement of the protozoa
+**Also acts in a phagocytic manner surrounding food particles and enclosing it in a vacuole
+**E.g. ''Entamoeba''
+*Gliding
+**No obvious means of locomotion
+**E.g. ''Eimeria''
+==Nutrition and digestion==
+[[Image:Pinocytosis.jpg|thumb|right|150px|Pinocytosis - Mariana Ruiz Villarreal]]
+*Pinocytosis
+**Droplets of fluid taken into the cell
+**Generates small vesicles
+**Usually used for extracellular fluid ingestion
+**Requires ATP
+*Phagocytosis
+**Larger particles of matter taken into the cell
+**Usually solid particles ingested
+*Cell membrane envelops the fluid or food taking it into the cell
+*Lysosomes fuse with the fluid/food initiating digestion
+*Diffusion through the cell membrane allows excretion of metabolic products
+==Life Cycle==
+*Most protzoal reproduction is asexual using binary fission, schizogony and sporogony
+*Some protozoa also use sexual reproduction called gametogony
+*In some species, sexual and asexual reproduction occurs in the same host, whilst in others asexual reproduction occurs in the vertebrate host and sexual reproduction in the arthropod vector
+*Homogenous
+**Parasite uses a single host species during its life cycle (direct)
+**E.g. ''Eimeria''
+*Heteroxenous
+**Parasite uses more than one host during its life cycle (indirect)
+**E.g. ''Trypanosomes''
+*Facultatively heteroxenous
+**Parasite '''may''' use more than one host during its life cycle but this is not essential
+**E.g. ''Toxoplasma gondii''
+===Example Coccidian Life Cycle===
+''The following refers specifically to the life cycle of Coccidia spp.''
+==Protozoa of Veterinary Importance==
+[[Coccidia]]
+[[Tissue cyst-forming coccidia]]
+[[Piroplasmida]]
+[[Cryptosporidium]]
+[[Babesia]]
+''Leishmania'' involved in [[Parasitic skin infections - Pathology#Protozoa|skin infections]]